Pandemic Viruses Usually Adapt After Jumping to Humans, Study Finds

A study of seven recent outbreaks finds that most viruses crossing from animals to humans did not show unusual pre-jump mutations; once they infected humans, they underwent rapid adaptation for human transmission. SARS-CoV-2 followed this pattern, while the 1977 Russian flu appears to be an exception with evidence suggesting a lab-related origin. The findings support animal origins for Covid and highlight ongoing zoonotic risk.